1. Field of the Invention
The invention relates to a backlight module; in particular, a backlight module that can maintain its image quality after a shock.
2. Description of the Related Art
Liquid crystal displays (LCDs) are gaining popularity for use in systems such as television receivers, computer monitors, avionics displays, aerospace displays, and other military-related displays where the elimination of cathode ray tube (CRT) technology is desirable for several reasons. In particular, CRTs are characterized by large depth dimensions, undesirable weight, and fragility. Additionally, CRTs require a relatively high voltage power supply in order to sufficiently accelerate electron beams for displaying images.
In general, LCD devices have various advantages in comparison with CRT display devices in that they are thin and low in power consumption, etc. Therefore, such LCD devices might be expected to be substituted for CRT display devices and have been a matter of great interest in some industry fields.
In contrast to the CRT, the liquid crystal display device requires a light source, because the liquid crystal is not a fluorescent material. A cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL) or the like is used as the light source of the liquid crystal display device. The lamp is included in a backlight unit of the liquid crystal display device. Backlight units are classified into direct back light type (or direct type) units and edge light type (or edge type) units, according to a position of the lamp.
In the case where the direct type backlight unit is used, incident rays from a lamp are directly incident to a liquid crystal display panel after a diffusion sheet uniformly diffuses the incident rays. In the case where the edge type backlight unit is used, rays from a lamp are incident to a liquid crystal display panel via a light guide plate. A detailed explanation of the edge type will be provided subsequently.
The edge type back light module generally includes a lamp, a light guide plate on a side surface of the lamp, a diffusion sheet on the top surface of the light guide plate, and a reflection sheet on the bottom surface of the light guide plate. The light guide plate uniformly scatters rays from the lamp such that rays are uniformly incident to the diffusion sheet. The reflection sheet reflects rays directed opposite the diffusion sheet such that most of the rays from the lamp are incident on the diffusion sheet. The diffusion sheet diffuses the rays to provide a uniform luminance throughout a light exit surface of the diffusion sheet. Additionally, a set of two prism sheets is beneficially disposed on the light exit surface of the diffusion sheet. The prism sheet set selectively changes the light rays as they pass through the sheets such that the luminance is enhanced at a particular viewing angle range. The rays from the prism sheet set are incident to the liquid crystal display panel of the liquid crystal display device such that images are displayed.
FIG. 1 is a partial cross-section of a conventional backlight unit 10. As stated above, a light guide plate 11 uniformly scatters rays from a cold cathode fluorescent lamp 12 such that rays are uniformly incident to the diffusion sheet (not shown). Thus, the light guide plate 11 is an element nearest to the cold cathode fluorescent lamp 12 in the backlight unit 10.
A Shock is an important reliability measure for LCDs. After the shock test, the structure of the LCD cannot be deformed seriously so that the light guide plate can be fixed to an original position in the LCD, and the backlight unit can maintain its image quality.
A frame of the liquid crystal display device supports the backlight unit including the above-mentioned sheets and lamp such that the liquid crystal display panel and backlight unit are fixed in a fixing structure. However, as the liquid crystal display device becomes thinner and thinner, the fixing or supporting structure of the above-mentioned backlight unit including the light guide plate et al. becomes more difficult to design. That is, space for fixing the backlight unit is so limited that a merely normal impact may break the fixing structure of the backlight unit.
FIG. 2a shows a conventional frame 22 supporting a light guide plate 21 of a conventional backlight unit. It is noted that the backlight unit has the light guide plate 21, and the frame 22 constitute the backlight module 20. As shown in FIG. 2b and FIG. 2c, the light guide plate 21 includes a protrusion 211, and the frame 22 includes a concave portion 221. By the protrusion 211 engaging with the concave portion 221, the light guide plate 21 is fixed to the frame 22. Generally, at the right side of the light guide plate 21 and the frame 22, the protrusion 211 and the concave portion 221 can be formed at any position except the position for screws (not shown). However, at the left side of the light guide plate 21 and the frame 22, except the position for screws, Y-TAB gate drivers (not shown) are also disposed. Thus, the protrusion 211 and the concave portion 221 can only be formed in positions without screws and gate drivers. It is noted that since the number of gate drivers is three to five, the space for the protrusion becomes smaller. Normally, the protrusion 211 can be only formed at the left-bottom corner of the light guide plate 21. Thus, the protrusion 211 of the light guide plate 21 is very small. During the shock, the contact area between the protrusion 211 and the concave portion 221 is also very small. As a result, the light guide plate 21 cannot resist the shock and can be broken, and the image quality of the backlight module is thus deteriorated. Furthermore, some of the light guide plates are totally damaged and moved so as to collide with the lamp; therefore, the lamp is also broken so as to not perform properly as the light source.
FIG. 3 shows another conventional frame 32 supporting another conventional light guide plate 31. As shown in FIG. 3, in such conventional backlight module 30, the light guide plate 31 is provided with two notches 311 at its bottom. The frame 32 is provided with two protrusions 321 corresponding to the notches 311 so as to prevent the light guide plate 31 from moving. By the protrusions 321 holding the notches 311, the light guide plate 31 can be prevented from breaking so that the lamp is not broken. However, since the light guide plate 31 linearly contacts with the frame 32, the light guide plate 31 may generate a crack 50 during the shock test. Such crack 50 may affect the image quality of the backlight module.
It is understood that in some backlight module, the light guide plate is adhered to the reflection sheet and then the reflection sheet is adhered to the frame. Such light guide plate is not provided with protrusions. Since the adhesive is disposed between the light guide plate and the frame, it may affect the image quality of the backlight module at high temperatures.
It is noted that the light guide plate 21, 31 is simply positioned in the frame 22, 32, and is not fixed therein. However, after the whole backlight module is assembled, the light guide plate is immobilized by the presence of other elements well known by those skilled in the art, thus description is omitted.
In order to address the disadvantages of the aforementioned backlight module, the invention provides a backlight module that can maintain image quality after a shock.
Another purpose of this invention is to provide a backlight module with a frame and a light guide plate stably disposed in the frame.
Accordingly, the invention provides a backlight module comprising a hollow frame and a light guide plate. The hollow frame includes a first protrusion that projects inwardly inside the hollow frame. The light guide plate, including a concave portion at a side of the light guide plate corresponding to the first protrusion, is disposed in the hollow frame in a manner such that the first protrusion engages with the concave portion.
In a preferred embodiment, the light guide plate further includes a second protrusion at the side, and the second protrusion is substantially longer than a quarter of a length of the side.
Furthermore, the length of the second protrusion may be substantially equal to half of the length of the side.
In another preferred embodiment, the light guide plate includes a curved surface connecting the second protrusion and the concave portion.
Furthermore, a tangent of the curved surface intersects the frame at an angle substantially less than forty-five degrees.
It is understood that corners of the second protrusion may be rounded, and the frame may be made of plastic.
In another preferred embodiment, this invention provides a backlight module. The backlight module comprises a hollow frame and a light guide plate. The hollow frame includes a concave portion. The light guide plate, including a protrusion at a side of the light guide plate, is disposed in the hollow frame in a manner such that the protrusion engages with the concave portion.